This invention relates to a sound system comprising at least one monitoring device, a source device and a transmission medium.
Sound systems are sound systems informing and entertaining a public in buildings or public places, for example airports or railway stations. These systems can also be used for warning the public in any emergency events. Such sound systems comprise several loudspeakers and amplifiers. The loudspeakers are often arranged in lines. For a good performance it is necessary to monitor the connection and correctness of the loudspeakers and the lines.
To supervise sound systems, there are several techniques known in the state of the art. For example, it is possible to supervise the loudspeaker line using a DC-signal, since the DC-signal is not converted to acoustical sound waves by a loudspeaker. Loudspeakers using this technique need an extra component in their design, such that the DC-signal is not shorted by the loudspeaker coil. This makes an existing sound system difficult to upgrade. There is also the possibility to supervise the sound system using AC-signals. Since an AC-signal is converted to acoustical sound waves by the loudspeakers, such signals are used in a frequency range, where they are not audible for the human ear.
Most supervising systems are used as end of the line devices, which are connected at the end of a loudspeaker line. These devices either detect the supervision signal and send back a different signal or it forms a load, which can be detected. If the end of the line devices are forming a load, they have to be calibrated to the cable length and therefore tested in the field.
The document DE 10 2010 028 022 A1, which seems to be the closest state of the art, describes a technique for supervising a loudspeaker line. The loudspeaker line connects a first point (main module) with a second point (supervising module). Main module and supervising module are able to communicate with each other. The loudspeaker line has an impedance, which can be variated by a communication partner to transmit a digital communication signal.